C-PIE II ABSTRACT Multidrug-resistant organisms (MDROs) are increasingly common causes of healthcare-associated infections (HAIs), complicating treatment and leading to increased morbidity, mortality and cost. The Chicago Prevention and Epicenter II (C-PIE II) has developed a portfolio of research projects to study the epidemiology and prevention of key HAI problems, i.e. those caused by MDROs, from the level of individual intensive care units to entire healthcare facilities (long-term acute care hospitals) to the region (Chicago, the third largest city in the nation) and to the state (Illinois, population 13 million). Our proposals range from investigations to improve basic infection control interventions that we have pioneered, such as chlorhexidine gluconate (CHG) bathing, to research that employs the most advanced molecular diagnostic techniques, e.g. bacterial whole genome sequencing and microbiome analysis, and cutting-edge informatics and analytic methods, such as automated alerts and social network analysis. We will conduct our work within a sophisticated existing infrastructure of strong collaborative public health and academic partnerships. These proposed activities comprise our Core Project and Multicenter Collaborative Project proposals. Core Project: We will continue to evaluate novel methods to study the epidemiology and control of carbapenem-resistant Enterobacteriaceae, to optimize antimicrobial stewardship interventions through ethnographic evaluation, and to assess the effect of alternative nasal decolonization strategies on the susceptibility of methicillin-resistant Staphylococcus aureus to antibiotics and antiseptics. The likelihood of success of our investigations is increased by our plan to use a coordinated, collaborative approach across many healthcare facility types, public health agencies, and academic institutions. Multicenter Projects: We propose a Large-sized Collaborative Project (MAriMbA) that will test the hypothesis that specific host factors, clinical care exposures, and gut microbiota alterations are associated with an increased risk of colonization by enteric MDROs. We propose a Medium-sized Collaborative Project (DataMAP-AU) to promote an infrastructure that can be expanded nationally to facilitate and standardize antimicrobial use metrics that are most informative for antimicrobial stewardship interventions. We propose a Small Collaborative Project (CHECkuP) to better understand the optimal use of CHG skin antisepsis to reduce patient colonization by MDROs. In total, we expect our work to fill critical gaps in knowledge related to the epidemiology and prevention of HAIs caused by MDROs, and to advance the science of infection prevention.